1. Field of the Invention
This invention relates generally to effluent filters for use in septic tank and other on-site waste disposal systems and, more specifically, to an effluent filter of increased longevity, having a stepped inlet side and a stepped outlet side that define a lower first filter zone and an upper second filter zone, to prevent particles from passing through the effluent filter on the outlet side.
2. Description of the Prior Art
Many homes, parks, and commercial developments throughout the United States lack municipal sewer services due to their remote locations, or owner preference. Instead, such locations utilize on-site waste and septic tank systems for their sewage disposal needs. Septic tanks include at least one entry port to accept sewage waste from a nearby home or commercial structure, and at least one effluent port. The septic tank typically holds an upper scum layer, an intermediate liquid effluent layer called the clear zone, and a lower sludge layer. Grease, fats, oils and floatables are typically found in the scum layer. The sludge layer is where most of the solid waste products collect and biologically decompose.
Particles from the sludge layer tend to float up into the clear zone, in part because the specific gravity of most such particles is less than 1. There have been many past attempts to design effluent filters to filter these particles out of the liquid effluent before the effluent is discharged from the septic tank. All such prior art effluent filters have been, in effect, "one-pass" filters, in that there is basically only one opportunity for particles to be caught in slits, holes, or mesh of the filter before the effluent is discharged from the septic tank.
An example of a first type of one-pass effluent filter is shown in U.S. Pat. No. 5,382,357. This effluent filter includes a tubular element having many slots therein to trap particles that are floating in the liquid effluent. The tubular element is disposed entirely within a standard T baffle (also called a pipe T) of a septic tank, or at least entirely within a vertical length of pipe extending from the T baffle. The tubular is element has an open lowermost end. A separate sealing gasket is provided at the bottom of the tubular element to provide a seal between the outer wall of the tubular element and the inner wall of the T baffle. The effluent is intended to be forced to flow into an open lower end of the T baffle or the vertical length of pipe associated with the T baffle, and into the open lowermost end of the tubular element of the effluent filter. In order for the effluent to reach the outlet port of the T baffle and thereafter be drained away from the septic tank, the effluent must first pass through the slots of the tubular element, i.e. from inside to outside the effluent filter. The slots are sized so that particles of at least about 1/16th inch are caught by the slots, and thereby filtered out of the effluent.
The integrity of the seal between the tubular element and the wall is dependent upon the precision of the diameter and shape of both the T baffle and the tubular element at a single specific region of the tubular element. If, for example, the T baffle is slightly out-of-round at the particular point at which the sealing gasket is intended to interface with the vertical portion of the inner wall of the T baffle, the effluent filter can be bypassed entirely by the particles in the effluent, rendering the filter virtually useless. This is because there is only a single annular gasket provided on the tubular element to provide a seal between the inner wall of the T baffle and the tubular element. If the gasket does not form a sufficiently tight seal, which can occur if either the T baffle or the underlying portion of the tubular element is out of round at the point of interface, particles will circumvent the effluent filter altogether. Also, an extra manufacturing step is necessary to install the separate sealing gasket onto the bottom end of the tubular element.
Another type of one-pass effluent filter is shown in U.S. Pat. No. 5,569,387. In this effluent filter, an elongated tubular element having slots therein is provided in a sanitary T baffle (also called a sanitary T, or a sweep T baffle). The elongated tubular element extends significantly below the lower end of the sanitary T baffle or any vertical pipe associated with the sanitary T baffle. Although not described in detail in the patent, a sealing gasket or ring is typically provided on the exterior of the elongated tubular element below the outlet port of the sanitary T baffle to provide a seal between the outer wall of the elongated tubular element and the inner wall of the sanitary T baffle. Above this sealing gasket, there are no slots in the elongated tubular element. Instead, there are openings in the wall of the elongated tubular element to permit filtered effluent to pass from inside the effluent filter to outside to be drained away from the septic tank.
The lowermost end of the elongated tubular element is closed, preventing effluent from entering through the bottom. Instead, effluent must be filtered through the slots in the wall of the elongated tubular element of the effluent filter, then travel up the length of the interior of the tubular element is before exiting through one of the openings above the sealing gasket or ring. This particular one-pass effluent filter shares the same shortcomings as the effluent filter previously described, in that the integrity of the seal can be compromised by a deformation of the sanitary T baffle at a single location where the sealing gasket is intended to engage the sanitary T baffle. Similarly, if the dimensions of the tubular elements for either type of effluent filter, or for the inner diameter of the sealing gaskets, are inaccurate, there may be an improper fit of the sealing gasket on the tubular element, providing a chance for non-filtered effluent to bypass the slots of the effluent filter. As with the previous effluent filter, the installation of the sealing gasket on the elongated tubular element requires an additional manufacturing step. Such one-pass effluent filters and their shortcomings are described in greater detail in the Detailed Description of the Preferred Embodiments and the Drawings.
Some effluent filters in the prior art make de minimis use of substantially horizontal filtering portions located at or near the top and bottom of the effluent filter, such as shown in U.S. Pat. No. Des. 402,349. However, this unit, too, is a one-pass effluent filter that suffers from the same disadvantages of the other single pass filters described above.
An additional shortcoming of these and other single pass effluent filters found in the prior art is that the filtering slits inherently become clogged relatively quickly, after which time the filter becomes useless and needs to be cleaned. It would therefore be desirable to provide an effluent filter that has increased longevity, in that even when certain portions of the effluent filter become clogged, the effluent filter is still effective elsewhere in the filtration of particles.
It would further be desirable for an effluent filter to be made as a single piece in a single manufacturing operation, so as to reduce production time, reduce manufacturing and labor costs, reduce the number of components needed for installation, and also reduce requirements of high tolerances (such as for the interior diameters of annular gaskets that need to be installed on prior art effluent filters), and finally, to increase the rate of production of effluent filters.
Furthermore, effluent filters that have separate single sealing gaskets often do not have adequate friction from the sealing gaskets to hold the effluent filter in place within a vertical section of pipe, such as PVC or polyethylene pipe, or a T baffle, particularly if the section of pipe or the T baffle has an irregular, uneven interior surface at the desired location of interface between the gasket and the section of pipe or T baffle. Thus, another desirable feature for an effluent filter would be to provide an integral means for providing increased friction between the effluent filter and the associated section of pipe and the T baffle in which the effluent filter is located.
The manner in which the present invention overcomes these and other shortcomings of the prior art, and achieves the desirable features of an effluent filter described above, is described in the following Summary of the Invention, Drawings, and Detailed Description of the Preferred Embodiments.